Method and device for processing data packets

ABSTRACT

The invention proposes a method of encoding data packet by encoding type information and size information of said data packet into the same field. The invention also proposes a method of processing data packets received. The data packet comprises a header part and a message part. The header part comprises at least one bit for indicating the type of said data packet, said method comprising a step 101 of obtaining the size information of said data packet based on said at least one bit.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of a U.S. application Ser. No.17/016,756 filed on Sep. 10, 2020, which is a continuation of a U.S.Pat. No. 10,791,204 filed on Apr. 5, 2018, which is a continuation ofU.S. Pat. No. 10,694,008 filed on Dec. 20, 2011 which is the U.S.National Phase application under 35 U.S.C. § 371 of InternationalApplication No. PCT/IB2010/052580, filed on Jun. 10, 2010, which claimsthe benefit of EP Patent Application No. EP 09163713.2, filed on Jun.25, 2009. These applications are hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to the communication of two devices, moreparticularly, to processing data packets transmitted from a seconddevice to a first device.

BACKGROUND OF THE INVENTION

The transmission of information from one device to another device occursin all sorts of technical fields; for example, information istransmitted via data packets from one mobile phone to another, or from aserver to a client, etc. Data packets can be transmitted via wire, forexample, telephone line, network line, etc. Data packets can also betransmitted wirelessly, for example, using near field communication(NFC) technology, or using satellite communication technology, etc.

A data packet typically comprises a header part and a message part. Theheader part is used for indicating some basic information related to thedata packet, such as: type of the data packet, size information (i.e.length) of the data packet, etc., which could also be understood as“metadata” or “overhead”. The message part is used for carrying themessage (i.e. information) that the data packet intends to carry.

In some cases, different types of data packet may have a different sizeof the message part. If the data packet needs to carry the sizeinformation of the data packet, typically, the header part is used tocarry this size information. The header part for example has twosections, one for indicating the type of the data packet, and anotherone for indicating size information of the data packet. As an example,the header part has two bytes, the first byte being for indicating typeinformation, and the second byte for indicating the size of the datapacket.

OBJECT AND SUMMARY OF THE INVENTION

However, in some other cases, since the data packet is required to be assmall as possible, the header part has a very limited number of bits andit has to be used for indicating the type of the data packet; and thereare no additional bits for indicating the size of the data packet.

For example, in a wireless power transmission system, a transmitter isused for transmitting power to a receiver inductively using at least oneprimary coil (transmission coil) and at least one secondary coil(receiving coil), and the receiver for example needs to send datapackets carrying configuration information to the transmitter, so thatthe transmitter knows the power requirement of the receiver and knowshow to configure the relevant parameters of the transmitter before thetransmitter can start to transmit power to the receiver.

One approach to transmit these configuration data packets is theso-called load modulation, i.e. the transmitter applies (transmits)power to the receiver and the receiver varies its power consumption inorder to encode binary signals i.e. data packets. In such a datatransmission approach, the duration required to transmit a data packetincreases by about 5.5 ms for each additional byte. Therefore, it isdesirable to keep the overhead on a data packet as small as possible. Asa consequence, the header part of this configuration data packet isdefined so as to comprise only a single byte. This byte is used forindicating the type of data packet. There is no extra byte forindicating the size of the data packet.

From a first aspect of this invention, it is advantageous to propose adata packet carrying size information of said data packet. The datapacket comprises a header part and a message part, said header partcomprising at least one bit for indicating the type of said data packet,wherein said at least one bit is also associated with size informationof said data packet.

From a second aspect of this invention, a method of encoding a datapacket having at least one bit for representing both type informationand size information of said packet is proposed; an encoder for encodingsuch a data packet is also proposed; and a device comprising the encoderis proposed. The device encodes the data packet and sends it to anotherdevice for communication with said other device.

From a third aspect of this invention, a method of processing datapackets received from a second device by a first device is proposed. Thedata packet comprises a header part and a message part. The header partcomprises at least one bit for indicating the type of said data packet.The method comprises a step of obtaining size information of said datapacket, based on said at least one bit which is used for indicating thetype of the data packet.

It is very useful to have the size information of a data packet. Forexample, if a transmitter does not know the size of the data packet, thetransmitter does not know whether the data packet is complete or not,and cannot locate the different parts of the data packet. Only when thesize information of the data packet is obtained, many different actionscan be implemented by the first device.

In the context of this invention, since sometimes the parts other thanthe message part of a data packet are fixed parts defined by a protocollike a standard, the size of the data packet depends on the size of themessage part of the data packet. In other words, as long as the size ofthe message part is known, the size of the data packet can be known andvice versa.

According to an embodiment of the invention, the method may furthercomprise a step of identifying said message part from said data packetaccording to the obtained size information.

According to an embodiment of the invention, said data packet furthercomprises a checksum part indicating a first value for verifying thecorrectness of the data packet. The checksum part can be locatedaccording to the obtained size information. The method further comprisesa step of calculating a second value, using the identified message part;and a step of determining whether said data packet is correct or not bycomparing said first value with said second value.

If the determining step determines that the data packet is incorrect;the method further comprises a step of discarding said data packet.

According to an embodiment of the invention, said data packet isassociated with an unknown packet type indicated by said at least onebit.

Normally, a protocol, e.g. a standard, defines many different datapacket types for communicating different kinds of information betweentwo devices. For some reason, e.g. to create the possibility of definingsome new message types in the future, in the previous version of theprotocol some values of the bits used for indicating the type of thedata packet are reserved for the future. How to define and use thesereserved values is not known at the time of defining the previousversion of the protocol; these reserved values probably will be defined(i.e. associated with a certain packet type) in the future version ofthe protocol, e.g. in the upgrade version. A newly defined packet whichis sent by the new generation device, is considered a type-unknownpacket when it is received by the old generation device.

In the context of this invention, if a device receiving a data packetknows what type this packet is, i.e. the header part is associated witha known packet type, this data packet is referred to as “type-knownpacket”; and if a device receiving a data packet does not know what typethis packet is, i.e. the header part of this packet is associated withan unknown type according to the knowledge of this device, this datapacket is referred to as a “type-unknown packet”. For example, theheader part for indicating the type information is one byte, of whichthe range from 0 to 180 is defined, and the range from 181 to 256 isreserved for future use: a data packet which has a header byte with avalue between 181 and 256 is called a type-unknown packet.

A type-unknown packet may be received for example if a device whichsends the packet is a new generation device in which some new packettypes are defined, however the device which receives the packet is anold generation device in which these new types defined in the newgeneration are undefined/reserved in the old generation.

Normally, when the old generation device receives a type-unknown packet,it will discard this packet immediately since nobody has realized thatthere is a need to know further information of a type-unknown packet.However, the inventor of this invention found that it would be useful toobtain the size information of such a type-unknown packet.

Therefore, according to an embodiment of the invention, a method isdisclosed of obtaining size information of a data packet of unknowntype. With the size information of such a type-unknown packet, someuseful steps can be implemented by the device receiving thistype-unknown packet.

According to an embodiment of this invention, the first devicecorresponds to a transmitter, the second device corresponds to areceiver, the transmitter transmits power to the receiver inductively;and the receiver sends the data packet by modulating the power drawnfrom said transmitter. If the data packet is associated with an unknownpacket type according to the at least one bit, and if the determiningstep determines that the data packet is incorrect; the method furthercomprises a step of aborting the transmission of power to the receiver.

From a fourth aspect of this invention, a first device is proposed forprocessing a data packet received from a second device. The data packetcomprises a header part and a message part. The header part comprises atleast one bit for indicating the type of said data packet. The firstdevice comprises a first unit for obtaining the size of said datapacket, based on said at least one bit.

According to an embodiment of this invention, the first device furthercomprises a second unit for identifying said message part from said datapacket according to the obtained size information.

According to an embodiment of this invention, wherein said data packetfurther comprises a checksum part indicating a first value, the firstdevice further comprises a third unit for calculating a second value,using said identified message part, and a fourth unit for determiningwhether said data packet is correct or not by comparing said secondvalue with said first value. The second unit calculates the second valueaccording to an exclusive-or algorithm.

According to an embodiment of this invention, the first device furthercomprises a fifth unit for discarding the data packet when it isdetermined that the data packet is incorrect.

According to an embodiment of this invention, wherein the first devicecorresponds to a transmitter, and the second device corresponds to areceiver, the transmitter transmits power to the receiver inductively;the receiver sends a data packet by modulating the power drawn from saidtransmitter; and the data packet is associated with an unknown packettype according to said at least one bit. The first device furthercomprises a sixth unit for aborting the transmission of power when it isdetermined that the data packet is incorrect.

From a fifth aspect of this invention, a data packet is proposed. Thedata packet comprises a header part and a message part, the header partcomprising at least one bit for indicating the type of said data packet,and at least one bit is also associated with size information of saiddata packet. The data packet may also comprise a checksum part forverifying whether the data packet is correct or not.

These and other characteristics, features and advantages of the presentinvention will become apparent from the following detailed description,taken in conjunction with the accompanying drawings, which illustrate,by way of example, the principles of the invention. The description isgiven for the sake of example only, without limiting the scope of theinvention. The reference Figures quoted below refer to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail, and by way of example,with reference to the accompanying drawings wherein:

FIG. 1 shows a flowchart according to an embodiment of this invention;

FIG. 2 depicts an example of the structure of data packet 200;

FIG. 3 illustrates a block diagram of the first device 300.

The dotted lines in the Figures indicate related steps or blocks thatare optional; in some embodiments, these can be omitted.

Throughout the above drawings, like reference numerals will beunderstood to refer to like, similar or corresponding features orfunctions.

DETAILED DESCRIPTION

From the first aspect of the invention, a data packet comprising aheader part and a message part is proposed. The header part comprises atleast one bit for indicating the type of said data packet, and the atleast one bit is also associated with the size information of the datapacket.

In such a way, the size information of a data packet can be encoded intothe limited size of header part of said data packet and obtained by thedevice receiving that data packet. There are no additional dedicatedbits for indicating the size information of the data packet.

An encoder for encoding such a data packet is proposed. The encodercould be implemented by means of hardware or software, or both. Forexample it can be implemented by a memory stored with instruction codeor by a processor or a chip, etc.

A device comprising the aforementioned encoder is proposed, the devicecomprising a unit for sending the data packet to another device.

The association between the size information and the header part can beimplemented by introducing a look-up table stored in the devicereceiving the data packet. The look-up table lists the bits that areused for indicating the type of data packet and the size information ofthis data packet-type.

As indicated above, in many cases, since the message part is the onlypart whose size may be different depending on the type, the size of themessage part (also referred to as “length of the message part”) is theonly size information that needs to be encoded.

A concept of size classes can be used to indicate the size information,with a size class being a range of packet types which all have the samesize. For example, size class 1 means that the message part consists ofone byte, and size class 7 means that the message part consists of 7bytes. Assuming the header part has one byte, this provides for up to256 size classes, where each size class can have 1 . . . 256 packets(with the constraint that the total number of packets does not exceed256).

Table 1 shows an example of this implementation. It is to be noted thatonly column 1 and column 2 of table 1 are needed for implementing thisinvention. Column 3 is not necessary for the step of association sizeinformation to the header part; it is used just for the purpose ofillustrating the concept of the invention.

As shown in table 1, the header parts from 0x00 to 0x0F reflect amessage length of size class 1, which means that the packet typerepresented by any header part with a value from 0x00 to 0x0F has amessage part that consists of 1 byte. In this way, a device receiving adata packet can obtain the size information of the data packet fromtable 1.

From table 1, it can be seen that both the defined type and the reservedtype have been associated with size information. Therefore, a devicereceiving a type-unknown packet also can obtain the size information ofsuch a type-unknown packet; and if a new packet type with a 7-bytemessage part needs to be defined in an upgrade (future) version of aprotocol, one can select any of the reserved packet types from the groupof size class 7, i.e. the header part of the selected packet type havinga 7-byte message part should be in the range of values between 0x52 and0x57. As a result, although an old version device does not know thenewly defined packet type according to the old version look-up table,the old version device can get the size information of this unknown(undefined) packet. For example, for header byte 0x1F, although table 1shows that it is a “reserved” packet type, the size of its message partcan be obtained, which is 2.

This ensures forward compatibility with future releases without changesto the existing packet size and structure.

TABLE 1 Column 1 Column 2 Column 3 Header byte Size class Packet type0x00 1 Reserved 0x01 1 Signal Strength 0x02 1 End Power Transfer . . .0x05 1 Charge Status 0x06 1 Reserved . . . 1 Reserved 0x0F 1 Reserved0x10 2 Reserved . . . 2 Reserved 0x1F 2 Reserved . . . 0x50 Reserved0x51 7 Identification 0x52 7 Reserved . . . 7 Reserved 0x57 7 Reserved .. . 0xFC 31 Reserved 0xFD 31 Reserved 0xFE 32 Reserved 0xFF 32 Reserved

Since it will require substantial space to store the table thatassociates size information of the data packet with the header part(such as table 1), in an advantageous implementation, the sizeinformation can be calculated from the header part using a simpleformula, i.e. associating the size information with the header part viaa formula, e.g. the formula is: header/8+1, where the division is aninteger division (i.e. discarding any non-zero remainder; which meansfor a header with one byte for indicating the type of the data packet,the header having 256 different values representing 256 types, that thisformula provides for 32 size classes having 8 possible packet typeseach. For example, if the header is: 0x52, the size information shouldbe: 0x52/8+1=11, which means for example the message part is 11 bytes.

The formula can be different, based on how many size classes are neededand how many packet types are needed for each size class.

Without losing universality, in the following, the device receiving thedata packet is referred to as a first device, and the device for sendingthe data packet is referred to as a second device. The first device andthe second device could be any devices as long as the second device cansend data to the first device and the first device can receive the dataand interpret the data so as to perform the predefined action accordingto the received data. The methods and the first device for processingdata packets are illustrated in detail hereinafter by way of examplewithout limiting the protective scope of this invention.

FIG. 1 shows a flow chart of a method of processing a data packet by afirst device according to an embodiment of this invention.

FIG. 2 shows an example of the structure of the data packet 200. Thedata packet 200 consists of four parts, namely, preamble part 201,header part 202, message part 203 and checksum part 204. The pre-amblepart 201 signals the start of a data packet. The header part 202indicates the type and size of the data packet. The message part 203carries the message that the second device intends to transmit to thefirst device. The checksum part 204 is intended to be used to verifywhether the data packet 200 is correct or not by means of the firstdevice.

The first part that follows after the preamble 201 is the header part202. The header part 202 is used to indicate the type of the data packet200; in the scenario of this invention, the header part is assumed to besmall; it has for example only 8 bits (1 byte).

The header part 202 is followed by the message part 203. The messagepart 203 has multiple bits for carrying the message. As indicated above,for different types of data packet, the size of the message part may bedifferent. Some packet types may only need 1 byte as message part, whileother packet types may need much more than 1 byte for carrying amessage.

FIG. 3 schematically illustrates a block diagram of a first device 300.

Now, referring to FIGS. 1˜3, the first device 300 comprises a memory 307for storing the data packet 200 which is received from a second device.The received data packet 200 comprises a header part 202 and a messagepart 203. The header part 202 comprises at least one bit for indicatingthe type of said data packet, e.g. the header part 202 has 1 byte (b₀,b₁, . . . , b₇) for indicating the type of the data packet 200. Thefirst device 300 comprises a first unit 301 for performing a step 101 ofobtaining the size information of said data packet 200 based on b₀˜b₇.

Optionally, the obtaining step 101 can be performed by checking alook-up table associating b₀˜b₇ with the size information of the packet200. The look-up table should be pre-stored in the first device 300. Anexample of such a look-up table is column 1 and column 2 of table 1. Forexample, according to table 1, for the value of 0xFC, the size of themessage part is in class 31, which means for example the message parthas 31 bytes.

Advantageously, the obtaining step 101 can be performed by calculatingthe size of the packet, based on the value of the header part 202according to a predefined formula pre-stored in the first device 300.

Table 2 shows an example of the pre-stored formulas for calculating thesize of the packet (size of the message part) according to the value ofthe header part 202.

TABLE 2 Header Message Size 0x00~0x1F 1 + (header − 0)/32 0x20~0x7F  2 +(header − 32)/16  0x80~0xDF  8 + (header − 128)/8 0xE0~0xFF 20 + (header− 224)/4

As shown in table 2, for header part values from 0x20 to 0x7F, theformula for calculating the size of the message part is(2+(header−32)/16). For example, if the header part 202 is 0x52, thesize of the message part of packet 200 should be:2+(0x52−32)/16=2+(82−32)/16=5, which means that the size of the messagepart of packet 200 is 5 bytes (40 bits).

Knowing the size information of the data packet 200, it helps toidentify (locate) the different parts of the packet.

Advantageously, the first device 300 may comprise a second unit 302 forperforming a step 102 of identifying said message part from said datapacket according to the obtained size information. As a result, whichbits belong to the message part 203 and which bits belong to thechecksum part can be determined. In other words, the message part can belocated.

When the different parts of the data packet are located, the firstdevice 300 is then able to further perform some actions. For example,knowing which bits belong to the checksum byte, the first device then isable to verify the correctness of the received data packet 200.

Advantageously, the first device 300 comprises a third unit 303 forperforming a step 103 of calculating a second value according to theidentified message part; a fourth unit 304 for performing a step 104 ofdetermining whether said data packet is correct or not by comparing afirst value indicated by the checksum part 204 with the calculatedsecond value.

The checksum part has a fixed-size datum computed from an arbitraryblock of digital data for the purpose of detecting accidental errorsthat may have been introduced during its transmission or storage. Theintegrity of the data packet can be checked at any later time byre-computing the checksum value and comparing it with the stored one. Ifthe checksums do not match, the data was almost certainly altered(either intentionally or unintentionally). The procedure that yields thechecksum from the data is called a checksum function or checksumalgorithm. A good checksum algorithm will yield a different result withhigh probability when the data is accidentally corrupted; if thechecksums match, the data is very likely to be free of accidentalerrors.

The checksum part 204 comprises for example a single byte indicating afirst value for verifying whether the data packet 200 is correct or not,i.e to verify whether the data packet 200 has been received correctly ornot after the packet 200 is received by the first device from the seconddevice.

To determine whether the packet 200 is correct, firstly, the firstdevice has to retrieve the first value from the checksum part 204. Sincethe checksum part 204 follows the message part 203, the checksum byte204 can be located when the message part 203 is located.

The first value represented by the checksum byte 204 is calculatedaccording to a predefined algorithm by the second device and is added tothe packet 200 as the checksum byte before the packet 200 is sent to thefirst device 300. If the first device 300 calculates the second valueaccording to the same predefined algorithm, the second value should bethe same as the first value. If the two checksum values are the same,the packet 200 has been transmitted correctly, i.e the packet 200 iscorrect; however, if they are not the same, there has been atransmission error during the transmission of the packet.

There are many algorithms for calculating the first and second value,for example, the longitudinal parity check, which breaks the data into“words” with a fixed number n of bits, and then computes theexclusive-or (referred to as XOR) of all those words. The result isappended to the packet as an extra word. To check the integrity of amessage, the first device computes the exclusive-or of all its words(header byte, message part, and checksum byte); if the result is not aword with n zeros, the first device knows that a transmission erroroccurred.

As an example, the algorithm is: header byte XOR 1st message byte XOR2nd message byte XOR . . . XOR last message byte. Consider for examplethe byte sequence 0x23 0x10 0x35 0x06 0x45. The packet starts at thefirst byte of the sequence, i.e. the header byte is 0x23. This meansthat the size of the message in the packet is 2 bytes according to table2, i.e. 0x10 0x35. The byte following the message is the checksum, i.e.0x06, which is calculated as 0x23 XOR 0x10 XOR 0x35. The last byte inthe sequence (i.e. 0x45) is not actually part of the packet (and wouldbe ignored by a transmitter).

Alternatively, any other known checksum algorithms could be used.

Advantageously, the first device further comprises a fifth unit 305 forperforming a step 105 of discarding said data packet 200 when the fourthunit 304 determines that the data packet 200 is incorrect.

Since the packet 200 has been verified to be incorrect, the transmitterhas to discard the data packet and wait for the next data packet,irrespective of whether the received data packet is a type-known packetor a type-unknown packet.

If the header part 202 corresponds to a type-unknown packet, it meansthe first device 300 does not know which type the data packet 200 is,and therefore the first device 300 cannot make use of this data packet.In this case, the first device has to discard the received data packet200 no matter whether the packet is correct or incorrect so as to ensurethat a first generation of e.g. transmitter would remain compatible withfuture generations of receivers.

Advantageously, the first device 300 corresponds to a transmitter, thesecond device corresponds to a receiver. The transmitter comprises oneor more primary coils which are coupled with one or more secondary coilsof the receiver. The primary coil is applied to an AC power source togenerate a magnetic field which will induce a voltage in the secondarycoils; in such a way, the transmitter can transmit power to thereceiver. When the transmitter applies power to the receiver, thereceiver can send data packet 300 by modulating the power drawn fromsaid transmitter, i.e. by varying the power consumed from saidtransmitter. The first device 300 further comprises a sixth unit 306 forperforming a step 106 of aborting the transmission of power when thefourth unit 304 determines that the data packet is incorrect. If thedata packet 200 is sent in this way, the incorrectness of the datapacket 200 indicates a power transmission problem since the data packetis modulated onto the power signal.

There are numerous ways of implementing functions by means of items ofhardware or software, or both. In this respect, the drawings are alsovery illustrative, each representing only one possible embodiment of theinvention. For example, the above-mentioned unit 301, 302, 303, 304,305, 306 can be implemented by one or a plurality of memories storedwith different instruction codes. These units may also be implemented byone or a plurality of printed circuit boards or by one or a plurality ofprocessors.

It should be noted that the above described embodiments are given fordescribing rather than limiting the invention, and it is to beunderstood that modifications and variations may be resorted to withoutdeparting from the spirit and scope of the invention as those skilled inthe art readily understand. Such modifications and variations areconsidered to be within the scope of the invention and the appendedclaims. The protection scope of the invention is defined by theaccompanying claims. In addition, any of the reference numerals in theclaims should not be interpreted as a limitation to the claims. Use ofthe verb “comprise” and its conjugations does not exclude the presenceof elements or steps other than those stated in a claim. The indefinitearticle “a” or “an” preceding an element or step does not exclude thepresence of a plurality of such elements or steps.

What is claimed:
 1. A method of processing a data packet in a wirelesspower system, the method comprising: receiving a data packet from asecond wireless power device by a first wireless power device, whereinthe data packet comprises a header and a message, wherein the headerincludes a header value, wherein the header value indicates whether atype of the data packet is known to the first wireless power device;selecting a message size option from a plurality of message size optionsbased on the header value, wherein the message size options are arrangedto enable calculation of a size of the message based on the headervalue; and utilizing a size of the message, wherein the size of themessage is calculated based on the header value by applying a messagesize formula.
 2. The method as claimed in claim 1, wherein the messagesize formula is S=(Y+(X−Z)/Q), wherein S is the size of the data packet,wherein X is a value of a header part of the data packet, wherein Y isan integer value, wherein Z is an integer value, wherein Q is an integervalue.
 3. The method as claimed in claim 1, wherein plurality of messagesize options comprise a plurality of header values and associatedmessage sizes, wherein a look-up table comprises the plurality of headervalues and the associated message sizes, wherein the message size isselected from the look-up table.
 4. The method as claimed in claim 3,wherein the look-up table comprises: Header Value Range Message Length0x00~0x1F 1 + (Y − 0)/32 0x20~0x7F  2 + (Y − 32)/16  0x80~0xDF  8 + (Y −128)/8 0xE0~0xFF 20 + (Y − 224)/4

wherein the message lengths in the table are calculated according theequations and stored in the table, wherein Y corresponds to the headervalue.
 5. The method of claim 3, wherein the look-up table associates aplurality of header value ranges with a corresponding plurality ofmessage size options.
 6. The method as claimed in claim 1, furthercomprising: identifying a checksum of the data packet by the firstdevice, wherein the checksum indicates a first value; calculating asecond value based on the message by the first device; and determining,by the first device, whether the data packet is correct by comparing thesecond value and the first value.
 7. The method as claimed in claim 6,further comprising calculating the second value using an exclusive-or.8. The method as claimed in claim 6, further comprising discarding thedata packet when the data packet is incorrect.
 9. The method as claimedin claim 6, further comprising: inductively transmitting power from thefirst device to the second wireless power device; and abortingtransmission of the power to the second wireless power device from thefirst device when the data packet is determined to be incorrect; whereinthe data packet is received by decoding a modulation of a wireless powerfield, wherein the wireless power field is generated by the firstwireless power device.
 10. A computer program stored on a non-transitorymedium, wherein the computer program when executed on a processorperforms the method as claimed in claim
 1. 11. A first wireless powerdevice for processing a data packet received from a second wirelesspower device, the first wireless power device comprising: a memorycircuit, wherein the memory circuit is configured to store a pluralityof header values and an associated plurality of message size options,wherein the message size options are arranged to enable calculation of asize of a received data packet; and a processing circuitry, wherein theprocessing circuitry is configured to receive the data packet, whereinthe data packet comprises a header and a message, wherein the headercomprises a header value that indicates whether a type of the datapacket is known to the first wireless power device, wherein theprocessing circuitry is configured to select a message size option fromthe plurality of message size options, wherein the processing circuitryis configured to obtain a size of the message based on the header valueusing the selected message size option, wherein the size of the messageis calculated based on the header value by applying a message sizeformula.
 12. The first wireless power device as claimed in claim 11,wherein the message size formula is S=(Y+(X−Z)/Q), wherein S is the sizeof the data packet, wherein X is a value of a header part of the datapacket, wherein Y is an integer value, wherein Z is an integer value,wherein Q is an integer value.
 13. The first wireless power device asclaimed in claim 11, wherein the memory circuit is configured to storethe plurality of header values and associated message size options in alook-up table, wherein the processing circuitry is configured to selectthe message size option from the look-up table.
 14. The first wirelesspower device as claimed in claim 11, wherein the look-up tablecomprises: Header Value Range Message Length 0x00~0x1F 1 + (Y − 0)/320x20~0x7F  2 + (Y − 32)/16  0x80~0xDF  8 + (Y − 128)/8 0xE0~0xFF 20 + (Y− 224)/4

wherein the message lengths in the table are calculated according theequations and stored in the table,
 15. The first wireless power deviceof claim 14, wherein the look-up table associates a plurality of headervalue ranges with a corresponding plurality of message sizes.
 16. Thefirst wireless power device as claimed in claim 9, wherein theprocessing circuitry is configured to identify a checksum of the datapacket, wherein the processing circuitry is configured to calculate asecond value based on the message, wherein the processing circuitry isconfigured to determine whether the data packet is correct by comparingthe second value and the checksum.
 17. The first wireless power deviceas claimed in claim 11, wherein the processing circuitry is configuredto discard the data packet when the processing circuitry determines thatthe data packet is incorrect.
 18. The first wireless power device asclaimed in claim 17, wherein the processing circuitry is configured toreceive the data packet sent by the second wireless power device bydecoding a modulation of an electromagnetic field, wherein theelectromagnetic field is generated by the first wireless power device,wherein the processing circuitry is further configured to aborttransmitting the power when the processing circuitry determines that thedata packet is incorrect.
 19. A method of processing a data packet in awireless power system, the method comprising: receiving a data packetfrom a second wireless power device by a first wireless power device,wherein the data packet comprises a header and a message, wherein theheader includes a header value, wherein the header value indicateswhether a type of the data packet is known to the first wireless powerdevice; selecting a message size option from a plurality of message sizeoptions based on the header value; and selecting a size of the messagebased on the header value using the selected message size option. 20.The method as claimed in claim 19, wherein plurality of message sizeoptions comprise a plurality of header values and associated messagesizes, wherein a look-up table comprises the plurality of header valuesand the associated message sizes, wherein the message size is selectedfrom the look-up table.
 21. The method of claim 20, wherein the look-uptable associates a plurality of header value ranges with a correspondingplurality of message sizes.
 22. The method as claimed in claim 19,wherein the message size formula is S=(Y+(X−Z)/Q), wherein S is the sizeof the data packet, wherein X is a value of a header part of the datapacket, wherein Y is an integer value, wherein Z is an integer value,wherein Q is an integer value.
 23. The method as claimed in claim 19,wherein the look-up table comprises: Header Value Range Message Length0x00~0x1F 1 + (Y − 0)/32 0x20~0x7F  2 + (Y − 32)/16  0x80~0xDF  8 + (Y −128)/8 0xE0~0xFF 20 + (Y − 224)/4

wherein the message lengths in the table are calculated according theequations and stored in the table,
 24. The method as claimed in claim19, further comprising: identifying a checksum of the data packet by thefirst wireless power device, wherein the checksum indicates a firstvalue; calculating a second value based on the message by the firstwireless power device; and determining, by the first wireless powerdevice, whether the data packet is correct by comparing the second valueand the first value.
 25. The method as claimed in claim 24 furthercomprising: inductively transmitting power from the wireless power tothe second wireless power device; and aborting transmission of the powerto the second wireless power device from the first wireless power devicewhen the data packet is determined to be incorrect; wherein the datapacket is received by decoding a modulation of a wireless power field,wherein the wireless power field is generated by the first wirelesspower device.
 26. A computer program stored on a non-transitory medium,wherein the computer program when executed on a processor performs themethod as claimed in claim 19.